MochaAE - odd motion blur issue after tracking finished

I have to replace a logo on a pen that is being used in the shot. I have tracked it in MochaAE (and its not perfect but is acceptable).

Once the data is copied into AE, I am seeing a really weird behaviour - one frame before a large movement, the AEs built in Motion Blur starts to blur the new replacement graphic.
Looking at the keyframes, i can see no movement sufficient to cause this early blur. I have even tried copying the keys from the frame before and pasting to the affected one, and it makes no difference.

This early blur makes it blindingly obvious that the graphic is not attached to the video!

AE Motion Blur is set to the defaults.
The shot that was tracked is exactly he same file as the one in AE. Both projects are set to 25fps HD. The original material was conformed to 25fps in Cinema Tools before the original edit in FCP, then xml'd to AE.

Those numbers improved the blur on the dodgy frame, but actually made the rest of the track look really bad! However, you put me onto the right path, and a bit of fiddling with the comp setting has got a much improved overall shot.